1. Field
This invention relates to polycarbonates having improved thermal stability and to a process for preparing such polycarbonates.
2. Description of the Prior Art
In recent years, there has been extreme interest expressed in a class of high molecular weight polycarbonates formed by reacting an aliphatic or cycloaliphatic epoxide with carbon dioxide. These high molecular weight polycarbonates are useful as molding compositions in the formation of fibers and articles. Typically, the polycarbonates are produced by reacting an epoxide, e.g. ethylene oxide, propylene oxide, isobutylene oxide with carbon dioxide under pressure in the presence of an organometallic catalyst. Amplification of this description of the process is shown in U.S. Pat. No. 3,585,168, U.S. Pat. No. 3,900,424 and U.S. Pat. No. 3,953,383. Variations in this basic process are reported in U.S. Pat. No. 3,706,713, U.S. Pat. No. 3,689,462 and U.S. Pat. No. 3,699,079.
Hydroxyl groups on low molecular weight liquid polycarbonates of the type formed by reacting aromatic polyhydric alcohol and phosgene or those obtained by reacting a dihydric alcohol and bischlorocarbonate have been capped with monomers to form solid polymers. Examples of capping agents include disubstituted acids for formsing polyester-polycarbonates and isocyanates to form polyurethane-polycarbonates. Exemplary formulations are shown in U.S. Pat. Nos. 3,248,414; 2,999,844; 3,544,657, 3,897,391; and 3,689,462.